USING DEFORMATION TERRACES TO CONFINE THE SHORTENING AND UPLIFT OF THE LONGQUAN ANTICLINE

doi:10.3969/j.issn.0253-4967.2013.01.002

Abstract

Abstract:

Located at east of the Longmen Mountains Thrust,the Longquan anticline is a foreland uplift of Sichuan foreland basin. Three terraces have formed along the Kaijiang River across the Longquan anticline. According to optically stimulated luminescence (OSL) and ¹⁴C samples,the age of the terrace T₁ and T₂ is 4.6ka and (11.7?0.4)ka,respectively. With growing of the anticline,terrace surfaces deformed obviously,which is characterized by folding scarps.The longitudinal profiles of the terraces at the Kaijiang River have been measured by differential GPS.We interpret the subsurface fault and fold geometries using petroleum seismic reflection profiles,our data suggest that the Longquan anticline grows laterally through kink-band migration and depth-to-detachment is about 6 kilometers.The cumulative shortening along the direction of tectonic transport is estimated to be 0.8km. We can confine that the crustal shortening and the uplift rate in late Pleistocene is (1.36?0.41)mm/a and(0.64?0.19)mm/a. India colliding with Eurasia results in the strong resistance from the South China block against the E to SEE extrusion of Bayan Har block,most of the energy has released in the form of uplifting of Longmen Mountains,and part,by the decollement,has been transferred to form the Longquan anticline.The 12 May 2008 Wenchuan earthquake (M_W=7.9) of China occurred in the Longmen Shan thrust belt and is a consequence of the ongoing uplift process of the eastern margin of Tibetan plateau. After the earthquake,stress was reduced on the northern section and increased on the southern section of Longquan Fault.The event clearly illustrates that the Longquan anticline and the Longmen Shan thrust belt is an integral whole.The mechanism of uplift of Longquan Mountains provides some evidence for the orogenic model of brittle crustal thickening in the eastern Tibet Plateau.

Key words: Longmen Mountains, Longquan anticline, river terrace, crustal shortening and uplift

摘要：

位于龙门山逆冲推覆构造带东侧的龙泉山背斜,构成了四川前陆盆地的前陆隆起。通过室内航空相片对凯江跨背斜段的地貌面的解译,结合野外考察可知凯江发育3级阶地,其中T₁、T₂为堆积阶地,T₃为基座阶地。在野外用差分GPS测量了阶地的空间坐标信息,同时采集了各级阶地堆积物的测年样本,并经实验分析约束了阶地的形成年龄。另外,对石油地震剖面解译揭示出龙泉山背斜北段地壳缩短和隆升主要是通过褶皱膝折带迁移机制进行的,滑脱层的深度约6km。利用面积守恒准则计算出龙泉山背斜晚更新世以来的地壳缩短速率约为(1.36±0.41)mm/a、隆升速率为(0.64±0.19)mm/a。通过滑脱层的推覆抬升机制形成的龙泉山背斜,给青藏高原东缘变形模式中的逆断层推覆地壳缩短造山增加了证据。

关键词: 龙门山, 龙泉山背斜, 阶地, 地壳缩短和隆升

CLC Number:

P312.5

LI Kang, XU Xi-wei, TAN Xi-bin. USING DEFORMATION TERRACES TO CONFINE THE SHORTENING AND UPLIFT OF THE LONGQUAN ANTICLINE[J]. SEISMOLOGY AND GEOLOGY, 2013, 35(1): 22-36.

李康, 徐锡伟, 谭锡斌. 龙泉山背斜的地壳缩短与隆升——来自河流阶地变形的证据[J]. 地震地质, 2013, 35(1): 22-36.

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